1. Field of the Invention
This invention relates generally to the storage and transmission of images represented by logic signal groups and, more particularly, to a technique for substantial reduction in the number of logic signal groups required to reproduce an image without appreciable degradation of the image.
2. Description of the Related Art
In the representation of images, particularly those images to be displayed on cathode ray tubes, certain conventions have been instituted to insure compatibility of display systems. For example, an image can be represented by a two dimensional array of points or pixels, such as: (R.sub.xy, G.sub.xy, B.sub.xy) where:
R.sub.xy is the intensity of the red component at the point xy,
G.sub.xy is the intensity of the green component at the point xy, and
B.sub.xy is the intensity of the blue component at the point xy.
Equivalently, the image can also be represented by the array; EQU (Y.sub.xy, S.sub.xy, T.sub.xy) EQU where: EQU Y.sub.xy =0.299R.sub.xy +0.587G.sub.xy +0.114B.sub.xy =C.sub.R R.sub.xy +C.sub.G G.sub.xy +C.sub.B B.sub.xy, (1)
S.sub.xy =R.sub.xy -Y.sub.xy =0.701R.sub.xy -0.587G.sub.xy -0.114B.sub.xy, ( 2)
.eta. and EQU T.sub.xy =B.sub.xy -Y.sub.xy =-0.299R.sub.xy -0.587B.sub.xy +0.884B.sub.xy. ( 3)
Y.sub.xy is typically referred to as the luminance (parameter) of a pixel location or point, while S.sub.xy and T.sub.xy are typically referred to as the chrominance parameters. In either representation, three number parameters are associated with each point.
In a medium resolution system, 512 scan lines are employed and each scan line can consist of 512 points or pixel locations. If 24 bits are assigned to identify the color composition of each pixel (the industry standard), then approximately 800 KBytes of memory locations are required to store a single image. Related to the large amount of storage required for each image is the fact that at a 9600 Baud transmission rate, the image will require roughly 80 seconds to be transmitted.
While the image pixels are stored and transmitted in the luminance/chrominance representations, the RGB color parameters must be reconstructed for each pixel location when the image is to be displayed. The reverse transformation or decoding is given by the equations: EQU R.sub.xy =Y.sub.xy +S.sub.xy ( 4) EQU G.sub.xy =Y.sub.xy -0.509S.sub.xy -0.195T.sub.xy ( 5) EQU B.sub.xy =Y.sub.xy +T.sub.xy ( 6)
In order to reduce the size of the storage space needed to describe an image, it has been known in the related art to provide a method referring to frequently used pixel quantities in such a way as to reduce the repeated reference to these values or to encode the repeated values with shortened identifiers. These techniques have not been successful in appreciably reducing the amount of information needed to describe an image and, in addition, frequently require complex additional processing apparatus such as a full size frame buffer.
A need has therefore been felt for a technique of reducing or compressing the quantity of binary logic signals required to describe an image without serious degradation of the image. A need has also been felt for a technique for converting between the color parameter representation and the luminance/chrominance representation without lengthy computations.